The present invention relates generally to analog to digital converters and more particularly, to a system for externally referenced ratiometric signal processing.
Currently, many products use analog to digital converter circuits. The reason for this is that microprocessors analyze and use only digital data. Analog to digital converters are, therefore, necessary to convert electrical analog data to digital data.
As the need to convert analog data to digital data has increased, analog to digital converter circuits have become more sophisticated. Typical analog to digital converter circuits are no longer comprised of individual discrete components, but are instead comprised of integrated circuits and are capable of greater speed, resolution and accuracy.
Analog to digital (A/D) converters change signal voltages into digital numbers by comparing the signal voltages to an AID reference voltage. The resulting digital number represents the ratio of the signal voltage to the AID reference voltage. The A/D reference voltage is usually the supply voltage to the A/D, typically around five volts.
In cases where the incoming signal voltage is not ratiometric to the reference voltage, part to part variability of the A/D supply and reference voltage sources can cause variability in the digital representation of the signal voltage. A traditional method to address the reference voltage supply variability is to supply the reference voltage to the device generating the signal voltage. The device then uses the reference voltage source to compensate the signal voltage for part to part variability of the reference voltage source. Unfortunately, for analog circuits this usually involves using analog multipliers that add cost and complexity to the device and are also subject to temperature drift.
The disadvantages associated with this conventional A/D technique has made it apparent that a new technique for externally referenced ratiometric signal processing is needed. Preferably, the new technique would be able to accurately generate a signal voltage ratiometric to a reference voltage without the need for analog multipliers. The new technique should also not vary with different operating conditions.
It is, therefore, an object of the invention to provide an improved and reliable means for externally referenced ratiometric signal processing. Another object of the invention is to accurately generate a signal voltage ratiometric to a reference voltage without the need for analog multipliers.
In one aspect of the invention, a device for externally referenced ratiometric signal processing includes an external signal source and a control module. The external signal source has an external voltage reference supply for generating an external reference voltage and a gain and offset circuit for generating a signal voltage. The value of the signal voltage is varied so that the ratio of the signal voltage to the external reference voltage is proportional to the value of a physical phenomenon being measured by a transducer. The control module receives the signal voltage and the external voltage reference. The control module includes an analog to digital converter that converts the signal voltage to a digital signal. The digital signal is proportional to the ratio of the signal voltage to the external reference voltage. A microprocessor may then use the digital signal to determine the position of the transducer.
The present invention thus achieves an improved and reliable means for externally referenced ratiometric signal processing. Also, the present invention is advantageous in that the external voltage reference can be adjusted by the external signal source to communicate diagnostic information to the control module. The external voltage reference may also be adjusted by the control module to communicate information to the external signal source.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.